Method and apparatus for making thread chasers



Feb. 24, 1931. l,793,7,27

METHOD AND APPARATUS FOR MAKING THREAD CHASERS E. A. WALKER Filed March 8, 195o 2 Sheets-Sheet 2 Patented Feb. v24, 1931 UNITED s'rxrasl PATENT OFFICE? ERNEST A. WALKER, OF WORCESTER, MASSACHUSETTS, ASSIGNOR TO JOHN BATH, OF WORCESTER, MASSACHUSETTS METHOD AN D APPARATUS FOR MAKING THREAD CHASERS Application leqi March 8,

This invention relates to thread chasers which are commonly used in sets f three, four or more chasers equally spaced in a circular series.

It will be obvious that the teeth of such chasers will not be disposed in asingle plane but must be at successive positions along a helical path described about the axis of the work.

It is common practice to have the gauging abutment against which the chasers are clamped disposed normal to the axis of the work, and to manufacture the chasers in sets, with the gauging surfaces which co-operate with said abutment variably offset from the centers of the threads of the different chasers, so as to bring the threads into the desired helical path.

It is the general object of my invention to provide a method of producing thread chasers in quantity by which method an im'- proved article is attained at a reduced expense and by which method accurate interchangeability is accomplished.

A further 'object of my invention is to provide improved apparatus for use-in carrying out my improved method.

A preferred form of the invention is shown in the drawings, irl-which- Fig. l is a plan view of a portion of a grinding table used in carrying out my im' proved method;

Fig. 2 is a partial plan view of a set of spacing bars;

Fig. 3 is an end elevation of a clamping device for the thread chasers;

Fig. 4 is a side elevation thereof;

Fig. 5 is a detail plan View, looking in the direction of the arrow 5 in Fig. 3;

Fig. 6 is an end elevation of 'a modified form of clamping device; and

Figs. 7 to 10 illustrate my improved method of producing chasers in quantity.

In a prior patent to John Bath, No. 1,557 ,005, issued October 13, 1925, a process and apparatus is described by which a set of thread chasers can be producedwith their teeth properly offset to conform to the desired helical path when mounted in the usual holder. This method and apparatus has been 1930. Serin No. 434,391.

found satisfactory in producing thread chasers where the chasers were ground in setsv It has been found, however, that the'cor-i responding chasers in successive -sets often differed slightly, due to a small variation in the position of the edge of the grinding wheel after the operationl of the wheel trulng devices, or due particularly to the wear of the Wheel dressing tool or diamond point.

Variations due to these and other causes have made it impractical to use the chasers except in the sets in which they are ground, and have also made it impractical to attempt to replace a single damaged chaser in a set otherwise in good condition.

By proceeding as hereinafter set forth, each chaser of a set may be produced in quantity and all such chasers Will be exact duplicates. Sets may be assembled from such chasers regardless of the order in which they were ground.

In producing chasers by my improved method, I position a series of chasers C on a grinding table T by aligning the chasers against a spacing bar 20, which. in turn engages a Xed ledge or abutment 22 formed on or secured to the table T. The table T may be in the form of a magnetic chuck, or the chasers C may be otherwise firmly secured against the face of the spacing bar 20.

I provide the spacing bars 20 for the No. 1 chasers and I provide corresponding spacing bars 24, 25 and 26 for the No. 2, No. 3 and No. 4 chasers in a set.

In carrying out my improved method, I grind any desired number of No. 1 chasers by positioning them against the spacing bar 20 and I then replace the bar 20 by the'bars 24, 25 and 26 successively and grlnd a corresponding number of No. 2, No. 3 and No. 4

chasers against these successive spacing bars. All of the chasers thus produced will have accurately ground threads of correct pitch and cross section, but they may be subject to slight variations in position with respect to the gauging surface of the Chaser, as was the case when the chasers were ground in successive sets.

In order to produce chaserswhich are 'exact duplicates with respect to their gaugingy surfaces, I submitthe ground chasers t0 'aA further grinding operation .to be now deangularly disposed-"surfaces 31 and 32.- 'The i fixtures arel firmly clamped tothe table .T in any' convenient manner and maybe of such length as to receive anyl desired number of previously ground chasers. i e l I `provide a series of spacing blocks 41,

'42, 43 and 44 (Figs. 7 to 10) corresponding to the No. l, No; .2, No. 3 and No.- 4 chasers. \nearer the gauging surface 32 of the fixture Each of these spacing blocks is provided with accurately finished upper and .lower surfaces v45 and 46 and with an intermediate surface 47. 2-

One of the spacing blocks 41 to 44 is placed Ain the clamping device against the finished surface 32 and a master locating plate 50 .is .clamped against the upper surface 45 thereof by clamping screws 52 (Figs. 3 and' 5). The locating 'or master plate is provided with accurately formed teeth along its outer face,

corresponding in pitch 1to the teeth of the thread chasers previously described.

In carrying out my process, a number of the No. 1 chasers C are placed against the master locating plate 50, with theirlower edge faces resting upon the intermediate surface 47 of the spacingblock 41. A clamping arm 60 is pivoted at 61 in a bracket 62 secured to the face of the fixture 30, and a stud 63 extends through a slot in the arm 60 and is provided with a convex washer 64 and a wing nut 65. By tightening the nut 65 the arm 60 is forced against the Chaser C, causing the teeth of lthe Chaser to be firmly seated in the teeth of the master plate 50.l

The intermediate surface 47.is so located that the Chaser C will be elevated slightly, away from the surface l47,. as it is clamped against the master plate 50, and is thus brought by a slight upward cam action int-o mesh with the thread grooves thereof. The

final vertical position of the Chaser depends entirely upon the position of the master 1ocating plate 50.

A grinding wheel W is trued up and positioned to grind an edge surface of the Chaser at an exact predetermined height above the table T. The wheel W is repeatedly adjusted and trued up as grinding operations proceed, so that the face of the wheel is maintained in the exact predetermined position.

After a number of Chasers have been clam ed against the master plate 50 on the gauglng fixture 30, the grinding wheel W is moved over the chasers and grlnds the edge l surface S thereof to an exact desired angle with the body of the Chaser and at a predetermined distance from the teeth of the master plate 50 and of thev chaser.

ing of the No. 2 chasers 'v *After all of the No. 1 chasers have been thus ground, the-spacing block 41 is removed and the block 42 is substituted, after which the master plate is clamped against the upper gauging surface 45 thereof and the grindproceeds as previous- 1y described.

If there are four chasers in av set to be produced, the surface 45 of the ,block 42 will be at a less height than the surface 45 of the block 41 by a difference corresponding to one quarter of the pitch of the threads to be Cut by the chasers. Consequently, the master plate 50 will be located that much 30 and the surface S of the finished Chaser will be offset one quarter of the pitch from the surface S of the No. 1 chasers. The No. 3 and No. 4 chasers are similarly produced ,by the useofvthe spacing blocks 43 and 44 vand are offset one half and three quarters of the pitch.

v1 Chaser may be assembled with any No. 2

Chaser, any No. 3 chaser and any No. 4 Chaser to produce a complete and accurate set of chasers. In the event of accident to any Chaser, any other Chaser of the same number may be substituted and the substituted Chaser will work accurately with the remaining chasers in the original set.

n Fig. 6 I have indicated a modified supporting structure in which two sets of chasers may be -ground at the same time. In this construction, a 'stand 70 is provided with a V- shaped master plate or block 71 which rests upon a spacing block 72 mounted in fixed -position on the stand 70. The master plate or block 71 is provided with thread grooves at each side to receive a pair of ground chasers 74 and 75 secured against the opposite faces thereof. c

Clamping arms 76 swing about pivots 77 at each side of the stand and may be drawn against the chasers 74 and 75 by a singlev clamping bolt 78 and wing nut 79. After the chasers havev been thus clamped in position, their upper edge surfaces are ground at a predetermined distance from the table on which the stand 70 is supported, as in the previous construction. The grinding operation may be performed by a single wheel'of suliicient width so that the two sets of vchasers are ground at a single operation.

When it is desired to shift operations from the No. 1 chasers to No. 2, No. 3 or No. 4 chasers, the No. 1 block 72 is removed and a corresponding block of different height is substituted, the height being proportioned to llO ously explained.

the particular chasers to be Having thus described my invention and- I e. the .method of producing chasers thereby, it

- what Iv claim is lengthwise of the chaser and parallel to the f will be evident that by the use of my invent tion, sets of chasers may be produced more economically than; with the previous .proi cedure, andthat the chasers-will possess the very valuable` feature" of accurate interL changeabilit-y, which has notv been heretofore accomplished inf the production of ground thread chasers.

Having thus described my invention and the advantages thereof, I do notwish to be limited to the details herein disclosed, other\ wise than as set forth in the claims, but 1. The method of producing a plurality of interchangeable thread chasers which con- Asists in preparing and hardening a plurality of thread chaser blanks, grinding a series of parallel thread grooves lengthwise in one face of all of said blanks, and inthereafter thread grooves and at the saine exact predetermined distance from said thread grooves in each -of said plurality of chasers.

2. The method of producing interchangeable thread chasers which consists in preparing and hardening a thread chaser blank,

grinding a series of parallel thread gropves lengthwise in one face thereof, placing said threaded chaser in a grinding position determined from the thread grooves, and'in thereafter grinding a side portion of said chaser vto provide a gauging surface extending lengthwise ofthe chaser and parallel tothe thread grooves and at an exact predetermined distance from said thread grooves.

3. The method of producing interchangeable thread chasers which consists in preparing and hardening a thread chaser blank,

rinding a series of parallel thread grooves ingthwise in one face thereof, providing a threaded master plate mounted in fixed position in a grinding machine, positioning the threaded chaser by its thread grooves against said master plate, and in thereafter grinding an edge portion of each chaser to provide a gauging surface at an exact predetermined distance from said thread grooves.

4. The method of producing interchangeable thread chasers in set'swhich consists in preparing and hardening a plurality of thread chaser blanks, grinding a series of arallel thread grooves lengthwise in one Eace of each blank, the approximate distance from the centers of the round threads to the gauging edge of the c asers varying according to the intended position of the chasers in a set, mounting said chasers on a supporting structure in grindin positions determined vfrom the ground t reads in said ground, as previa chasers, said grinding positions being varied `accordingto the intended position of the chasers in a set, and in grinding all of said chasers to provide gauging edge surfaces all in the same wheel.

5. Themethod ofproducing sets of interchangeable ground thread chasers which consists in providing aplurality of hardened thread chaser blanks, grindin parallel thread grooves ina group of sai blanks at an approximate predetermined distance from an edge surface of said blanks, grinding thread grooves in otherv groups of blanks at \other approximate predetermined distances from an edge surface of said blanks, the

plane relative to said grinding ber of chasers in a set, supporting the said ground chasers in positions determined solelyby the thread grooves ground therein, and in thereafter grinding an edge surface on veach chaser at an exact predetermined distance from the centers of the threads ground therein, whereby any chaser from one of said groups may be assembled with any chaser rom each of the other 'groups to form a set of interchangeable thread chasers. 6. T he method of making thread chasers to form sets-which comprise preparing a quantity of substantially duplicate chaser blanks, hardening said blanks, grinding thread grooves in said blanks at selected approximate distances from the edges of said blanks, and thereafter grinding a longitudinal edge of each chaser parallel to said thread grooves `and in an exact position determined from the thread grooves in said blank.

7. Mechanism for use in grinding a gauging edge surface on a thread chaser, comprising a supporting structure, a threaded master ment of the thread grooves of said chaser with the threads of the master plate.

8. Mechanism for use in grinding a gauging edge surface on a thread chaser, com-v prising a supporting structure having a gauging surface, a threaded master plate positioned by and against said spacin block, and means to clamp a ground threa chaser againstsaid master plate, the position of said chaser being determined by engagement of the thread grooves of said chaser with the threads of the master plate.

9. Mechanism for use in grinding a gauging edge surface on a thread chaser, comprising a supporting structure having a gauging surface, a series of spacing blocks any. one of which may be supported by said gauging surface, said blocks varying in thickness by proportional parts of the pitch of the thread of the chasers to be ground, a threaded master plate positioned by and abutting a selected spacing block, and means to clamp a, ground thread Chaser against said master plate, the position of said Chaser being determined by engagement of the thread grooves of said Chaser with the threads of the master plate.

In testimony whereof I have hereunto affixed my signature.

ERNEST A. VALKER. 

